The present invention relates to the transmission of data messages from a remote device to a data processing channel, and more particularly relates to an apparatus for decoding frames in data messages from a remote device to a data processing channel.
As is well known, data transmissions may be made from a remote device to a data processing channel wherein the data message is organized in frames having a header field and a trailer field. Devices are known which examine the header field to determine the type of message and contents of data in the data frame, and which examine the trailer field to identify the end of a frame or message.
U.S. Pat. No. 4,203,003 issued May 13, 1980 for "Frame Search Control for Digital Transmission System" to Kline, discloses a frame search control circuit which allows a comparison of up to N bits on the occurrence of each framing clock pulse while an out-of-frame conditions exists. The disclosed frame search control circuit stores the next N sequential bits for subsequent comparison, thus providing a fast reframe time.
U.S. Pat. No. 4,611,336 issued Sept. 9, 1986 for "Frame Synchronization for Distributed Framing Pattern in Electronic Communication Systems" to Fryer, discloses a frame bit synchronizer for a framing pattern sequence consisting of M bits distributed in a data bit stream as single bits at intervals of a fixed number N of bits, as measured from the start of one framing bit to the start of the next. The disclosed frame bit synchronizer includes counters which are cleared whenever a bit received is not the same as the next bit in the framing pattern sequence, and is incremented whenever a bit received is the same as the next bit in the framing pattern sequence. The count can be used as a threshold for determining when framing has occurred.
U.S. Pat. No. 4,651,319 issued Mar. 17, 1987 for "Multiplexing Arrangement with Fast Framing" to Bowlds, discloses a multiplexing arrangement for use in a digital communications system in which it is desired to multiplex plural user data inputs to a single serial digital communications channel, and then to decode the data to the appropriate user data outputs.
U.S. Pat. No. 4,674,088 issued June 16, 1987 for "Method and Apparatus for Detecting Frame Synchronization" by Grover, discloses a frame synchronization apparatus for detecting the framing pattern of a bit stream and producing a synchronizing slip in the absence of such detection.
U.S. Pat. No. 4,727,558 issued Feb. 23, 1988 for "Method and Apparatus for Extracting a Predetermined Bit Pattern from a Serial Bit Stream" to Hall, discloses locating an embedded frame bit pattern in a serial bit stream using a sliding compare circuit to determine, as each bit of the serial bit stream is received, if a predetermined number of prior bits in the serial bit stream which are spaced apart by the pitch of the framing bit pattern match part of the framing bit pattern.
U.S. Pat. No. 4,779,268 issued Oct. 18, 1988 for "Frame Decoding for Digital Signal Transmission" by Wissmann, discloses a method and apparatus for frame decoding in a system which has a series bit data flow with a frame structure including a periodically occurring item of synchronizing information which characterizes the start of each frame. A logic AND-link is performed with data in successive search frames until only one bit, the synchronizing bit, in the search frame is set at logic one and retained for a plurality of search frames.